Fibromyalgia (FM) is defined by a history of widespread pain, and the finding of tender points on examination. Arguably the two most discriminating features of FM are: 1) a generalized disturbance in pain perception, and 2) elevated levels of pro-nociceptive neuropeptides in the cerebrospinal fluid. The first feature, pain induced by a normally non-painful stimuli, is not surprising since this is a defining feature of FM. But it is not certain how tenderness relates to pain, since population based studies have demonstrated that not all persons who are tender have pain, and vice versa. And it has recently become clear that tender points are a poor measure of a person's inherent tenderness. The meaning of these elevated levels of CSF neuropeptides is likewise unclear. These findings may not be specific for FM, and may be the cause of pain and/or tenderness, or may be the result of pain, tenderness, or some other process. Chronic lower back pain (CLBP) is among the most common medical problems in industrial societies. Despite this, little is actually known about the precise cause for most cases of CLBP. Anatomic and psychosocial factors have been demonstrated to predict only a small portion of the variance in the degree of pain or disability in CLBP. In preliminary studies in CLBP, we have demonstrated that tenderness predicts a significant percentage of the variance in both functional status and pain, more than either the severity of path-anatomical abnormality (i.e., X-ray/MRI),or by psychosocial factors. In a small pilot study of a subset of these patients tenderness was correlated with CSF levels of pro-nociceptive neuropeptides. There are 3 specific aims in the proposed study: 1) To confirm in a cross-sectional study of 200 CLBP patients that pain sensitivity predicts more variance in clinical outcome (e.g. functional status, pain level, Roland index) than either anatomic or psychological factors. Furthermore, we will demonstrate that pain sensitivity is an independent trait, and not a surrogate for psychological factors such as depression, anxiety, or work-related stressors. 2) To demonstrate that an individual's global pain sensitivity is determined primarily by physiologic factors (e.g. neurotransmitters in cerebrospinal fluid) and modified by psychosocial factors (e.g. cognitive and behavior influences on pain perception). We will measure the CSF concentrations of pro-nociceptive peptides such as Substance P and Nerve Growth Factor, and hypothesize that the levels of these substances largely determine an individual's global pain sensitivity. This testing will be done in patients with CLBP and FM, as well as sedentary and non-healthcare-seeking controls. 3) To use alternative methods of pain assessment that are much less influenced by psychological factors (e.g., scaling methods, Multiple Random Staircase), using both pressure and thermal stimuli, to examine the true meaning of tender points, and the relationship between these results, and the results of the above noted physiologic and psychologic parameters in individuals with FM and CLBP.